Our current rig is 7 years old and it will be another couple of years before we get another. I don't worry about it's value since the RVing lifestyle is a losing proposition to say the least, we have used it extensively and will more than likely keep it in the family for our kids to use when we decide it's time for another.
We have been to many RV shows and current models don't differ much at all, we don't see a reason at this time to waste money on a new rig until we feel a need for change. No RV is perfect and all floorplans will have some pros and cons depending on your point of view.
It's a personal choice why we all decide it is time to look for a new rig, if it's something that is crossing your mind often it looks like a new rig is in your near future. Selling the 5er yourself may yield the highest return but some don't want to deal with the hassle and just trade in on a newer unit.
Biggest issue many encounter is believing their rig is worth more than what the market will bear, unless some sucker comes along they soon experience a reality check finding someone to bite. Dealers employ many tried and true tactics to make buyers believe they got a great deal, unfortunately that is rarely the case as they always get their profit margin, and in many cases much more.
No bones about it, the RVing lifestyle can be a costly venture, if you are happy with what your camper provides it may be wise to not forego your well kept rig at this current point. At 10 years you are definitely not alone considering something bright, shiny, and new, only you can decide if it is the right time.
Either way you go is bound to cost money in upkeep or a new payment, one thing for sure, when it comes to RVing, we all have to pay to play.